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Monday, April 18, 2016

Which animals are sentient?

Are spiders sentient? I took the above picture of a patient treated by my colleague Dr Stephen Cutter. The presenting complaint was mites. The use of insecticide spray as a treatment clearly had to be avoided.

Most of us assume companion animals have feelings that
matter, but to what extent is this true of other animals?

The term “sentience” is usually applied to an individual
who has the capacity to experience feelings. The word “feelings” has finally
become acceptable in animal welfare science – and not a moment too soon.
According to pioneering animal welfare scientist Professor Donald Broom, the
reluctance of some scientists to use what they feared were anthropomorphic
terms really put the brakes on animal welfare science for a good while:

“When scientists describe a complex system like the
brain, terms such as awareness, sentience, welfare, emotion and feeling should
be carefully defined and used. If they are not used, important aspects of
biological function are missed. The reluctance of some in the scientific
community to do this has slowed the development of knowledge.”(Broom, 2016)

According to Professor Broom, a sentient being is one
that is able to evaluate the actions of others in relation to itself and other
parties; to remember at least some of its own actions and their consequences;
to assess risks and benefits of a particular course of action; to have
feelings; and to have some degree of awareness.

If you think about it, there may be some human beings
(for example, very young or very old humans) who don’t exhibit the above
capacities. That is because, Broom says, sentience develops as we develop – and
it can also diminish or disappear, for example with age, illness or brain
injury.

Whether or not we recognise that an animal is sentient
has huge implications in terms of how we treat them. Our attitudes to animals
are affected by our evaluations of those animals abilities(Broom, 2010). We can just happen
to be very wrong in our assessments.

Which brings us back to our original question, which
animals are sentient?

Some people still think sentience is exclusive to humans.
That view just isn’t supported by science. As Professor Broom has said, “hardly
any ability is uniquely human(Broom, 2015).”

If you’re reading this blog, chances are you’re
comfortable that humans and most non-human companion animals like dogs and cats
are sentient. They can think, feel and suffer in ways we are generally able to
relate to. You may have seen evidence yourself of your dog looking for a toy
you’ve hidden, or your cat associating you walking into the kitchen with being
fed (examples of learning). They may behave in ways we describe as fearful or
sad. In fact, there is a huge body of research supporting the sentience of
parrots, dogs, pigs, cattle, sheep and other farm animals, laboratory animals,
wild mammals and birds.

Studies have found evidence of learning, awareness and
capacity for pain and other feelings in amphibians, fish, cephalopods (this
group includes octopus, squid and cuttlefish) and decapod crustaceans (crayfish,
crabs and lobsters, for example). There is also evidence of learning and
awareness in stomatopod

crustaceans (e.g. shrimp). (For a recent discussion on cephalopod cognition and
consciousness from a philosophical point of view, check out this article by
Joshua Shepherd reflecting on the escape of Inky the Octopus from a New Zealand
aquarium recently).

Spiders have “substantial cognitive ability” and
awareness, and some insects such as bees and ants have a high level of
cognitive ability and awareness.

While slugs, snails and swimming sea slugs have clear
evidence of a pain system, there is less clear evidence for a pain system in
insects and spiders – but the cognitive abilities of insects and spiders
exceeds those of slugs, snails and swimming sea slugs.

What does it all mean? Well, we’re not alone in the
sentience club. And as more studies come to light, it seems that membership is
very broad. Professor Broom argues that this scientific data needs to inform
our behaviour:

“All animal life should be respected, and studies of the
welfare of even the simplest invertebrate animals should be taken into account
when we interact with these animals. Even if we do not protect the animals by
law, we should try to avoid cutting an earthworm in half, mutilating a snail,
or damaging the wing of an insect.”

Veterinary Ethics: Navigating Tough Cases

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